Bone loss from the proximal femur continues into the nineties and low bone mass leads to an increased susceptibility to fracture. The risk of fracture accelerates between age 80-90 so that 33% of women and 17% of men sustain a hip fracture. Hip fractures cause an immediate 15% mortality, and will cost 20 billion dollars annually within 20 years. Two major factors play a role in the bone loss. Estrogen deficiency after the menopause is associated with increased bone loss from the femur. In the mid sixties a second factor emerges - malabsorption of calcium, which increases the degree of negative calcium balance causing secondary hyperparathyroidism and bone loss. By correcting estrogen deficiency and malabsorption of calcium it may be possible to reverse bone loss from the proximal femur. In order to test this hypothesis, 500 osteopenic women aged between 65-77 years will be treated with either estrogen, 1 alpha- hydroxyvitamin D2 (1 alpha-OH-D2) or a combination of estrogen and 1 alpha- OH-D2 for 3 years in an attempt to reverse bone loss from the proximal femur. It is suggested that estrogen will inhibit bone resorption and 1 alpha-OH-D2 will stimulate bone formation, and that the combination will be more effective than single therapy. The study will be double blind and placebo controlled. The primary outcome will be bone mineral density of the proximal femur, however, other areas of the skeleton will be measured so that any effect of therapy which might cause redistribution of bone mineral from cortex to trabecular sites can be detected. Loss of cortical bone could increase fracture susceptibility. Reversing bone loss from the proximal femur from age 65 for several years could maintain bone density above the fracture threshold and significantly reduce the risk of fracture. Not only would this provide considerable individual health benefits, but also greatly reduce health care costs.